VOLj LXXXIir.] PHILOSOPHICAL TRANSACTIONS. 331 



ticular attention. A series of observations on it, which I began in April 1777, 

 has been continued down to the present time. My first view, when I engaged 

 in the pursuit, was to ascertain the diurnal rotation of this planet, which, from 

 the contradictory accounts of Cassini and Bianchini, the former of which states 

 it at 23 hours, while the Iattermak.es it 24 days, appeared to remain unknown, 

 as to its real duration : for the observations of these gentlemen, how widely 

 different soever with regard to time, can leave no doubt but that this planet 

 actually has a motion oh its axis. 



The next object was the atmosphere of Venus ; of the existence of which also, 

 after a few months observations, I could not entertain the least doubt. The 

 investigation of the real diameter was the 3d object I had in view. To which 

 may be added, in the last place, an attention to the construction of the planet, 

 with regard to permanent appearances ; such as might be occasioned by, or 

 ascribed to, seas, continents, or mountains. 



The result of my observations would have been communicated long ago, if I 

 had not still flattered myself with the hopes of some better success, concerning 

 the diurnal motion of Venus ; which, on account of the density of the atmos- 

 phere of this planet, has still eluded my constant attention, as far as concerns its 

 period and direction. Even at this present time I should hesitate to give the 

 following extract from my journals, if it did not seem incumbent on me to 

 examine by what accident I came to overlook mountains in this planet, which are 

 said to be of such enormous height, as to exceed 4, 5, and even 6 times the 

 perpendicular elevation of Cimboracjo, the highest of our mountains !* 



The same paper, which contains the lines I have quoted, gives us likewise many 

 extraordinary accounts, equally wonderful; such as hints of the various and singular 

 properties of the atmosphere of Saturn. -f- A ragged margin in Venus, resembling 

 the uneven border of the moon, as it appears to a power magnifying from 1 

 to 4.;}: One cusp of Venus appearing pointed, and the other blunt, owing to the 

 shadow of some mountain.^ Flat spherical forms conspicuous on Saturn. || All 

 which being things of which I have never taken any notice, it will not be amiss 

 to show, by what follows, that neither want of attention, nor a deficiency of instru- 

 ments, could occasion my not perceiving these mountains of more than 23 miles in 

 height;** this jagged border of Venus ; and these flat spherical forms on Saturn. 



Indeed with regard to Saturn, I cannot hesitate a single moment to say, that 

 had any such things as flat spherical forms existed, they could not possibly have 

 escaped my notice, in the numberless observations with 7, 10, 20, and 40-feet 

 reflectors, which I have so often directed to that planet. However, if the gen- 



* See Phil. Trans., for 1792, part 2, page 337. t Ibidem, page 309. I p. 310. } p. 312. 

 II p. 336. ■** The height of Chinibo-ra^o, according to Mr. Condamine, is 3200 French toises : 

 and the English mile, by Mr. De Lalande, measures 830. If tlie mountains in Venus exceed 

 Chimbo-raf o six times in perpendicular elevation, they must be more than 23 miles in height. — Orig. 



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